One oilfield service major leads the ranked field with 192 patent families, more than three times the fifth-place count of 62. That leader’s filings are split across several corporate variants of the same group, which co-file frequently — the strongest co-assignee pairing shares 20 families. This concentration means the core sealing-pad and pretest-drawdown mechanics are heavily claimed by a small number of related entities, so a new entrant should expect to design around existing coverage rather than file into open space.

Filing peaked in 2018 at 28 records and has not returned to that level since. The leading assignee’s own filings fell from 5 in 2021 to 2 in 2024, a 60% drop over that span, but 2025 and 2026 data are still incomplete because publication typically lags filing by about 18 months. The honest read is that the field has settled below its 2018 peak, not that it is accelerating or collapsing in real time.

E21B, the earth and rock drilling wells classification, covers 88.1% of the 571 records in scope, confirming this is primarily a drilling-hardware field. G01N (material analysis, 16.6%) and G01V (geophysics, 14.4%) show a meaningful secondary presence of analytical and geophysical claims. Smaller classes — G01R, B01L, G06F, G06V and F04B — each sit under 5% and mark cross-disciplinary claims in electronics, lab apparatus, data processing, imaging and pumps that sit outside the mechanical core.